1. Field of the Invention
The present invention relates generally to electric switches having two or more stationary terminals and one or more movable bridging contacts adapted to be shifted into position to bridge the electrical connection between the stationary terminals, and more specifically to an electric switch of this type having a bridging contact that pivots about a roller element which is shiftable into two positions to enable the bridging contact to make electrical contact with a surface that is both different from the break surface of the fixed terminals and is not in the path of the bridging contact as the bridging contact slides along the break surface in order to avoid the problem of effecting the electrical make on top of contamination that has formed on the break surface thereof.
2. Description of the Prior Art
Toggle type switches in which an elongated bridging contact is positioned to be supported by, and rocked about, a central fixed terminal so that an end of the bridging contact can be shifted into engagement with a flat surface of a second fixed terminal, are in common use today. These switches commonly have a single fixed central terminal having a flat top surface thereof defining a fulcrum pivot point. The elongate bridging contact rides on this pivot point surface, and is adapted to rock upon this pivot point in order to selectively bridge the electrical contact between the two fixed terminals. The bridging contact is actuated by a spring loaded insulating plunger which is carried by the shank portion of a toggle mechanism, defining a bi-stable, over-center switching mechanism.
To shift the switching mechanism from one of its stable positions to the other stable position, the toggle element is moved, causing the elongate bridging contact to slide over the central terminal fulcrum point, compressing the insulating plunger up into the toggle shank. As the center line of the toggle and plunger mechanism crosses over the center line axis of the central terminal, the bridging contact is shifted away from the fixed terminal, effecting the contact break. In the reverse operation, the elongate bridging contact again rides over the center line axis of the central fixed terminal until the insulating plunger crosses over center, causing the bridging contact to snap back into electrical engagement with the fixed terminal.
The type of customary toggle switch described hereinabove utilizes a switching mechanism that causes the bridging contact and the stationary terminal to always make and break on the same surfaces. When the electrical contact is made and broken in this type of switch, an electric arc is generated between the two breaking contact elements, thereby depositing electrical contamination on each of these contact surfaces. After repeated breaks of the electrical contacts, this contamination has built up to such a degree that further positive make and break actions are made across these areas of contamination, rather than the initially smooth terminal surfaces, thereby resulting in extremely highly concentrated areas of current transfer across the build-up of contamination, further compounding the problem and contributing to the build-up of additional arcing contamination on each of these contact surfaces. This problem is, of course, greatly accelerated when the switch is used in high current applications.